DT: leds: Add binding for the ISSI IS31FL32xx family of LED controllers

This adds a binding description for the is31fl3236/35/18/16 I2C LED
controllers.
Signed-off-by: David Rivshin <drivshin@allworx.com>
Acked-by: Rob Herring <robh@kernel.org>
Signed-off-by: Jacek Anaszewski <j.anaszewski@samsung.com>

Documentation/devicetree/bindings/leds/leds-is31fl32xx.txt

+Binding for ISSI IS31FL32xx LED Drivers
+
+The IS31FL32xx family of LED drivers are I2C devices with multiple
+constant-current channels, each with independent 256-level PWM control.
+Each LED is represented as a sub-node of the device.
+
+Required properties:
+- compatible: one of
+	issi,is31fl3236
+	issi,is31fl3235
+	issi,is31fl3218
+	issi,is31fl3216
+- reg: I2C slave address
+- address-cells : must be 1
+- size-cells : must be 0
+
+LED sub-node properties:
+- reg : LED channel number (1..N)
+- label :  (optional)
+  see Documentation/devicetree/bindings/leds/common.txt
+- linux,default-trigger :  (optional)
+  see Documentation/devicetree/bindings/leds/common.txt
+
+
+Example:
+
+is31fl3236: led-controller@3c {
+	compatible = "issi,is31fl3236";
+	reg = <0x3c>;
+	#address-cells = <1>;
+	#size-cells = <0>;
+
+	led@1 {
+		reg = <1>;
+		label = "EB:blue:usr0";
+	};
+	led@2 {
+		reg = <2>;
+		label = "EB:blue:usr1";
+	};
+	...
+	led@36 {
+		reg = <36>;
+		label = "EB:blue:usr35";
+	};
+};
+
+For more product information please see the link below:
+http://www.issi.com/US/product-analog-fxled-driver.shtml